siman.
/ˈsʌɪmə/, U.S. /ˈsaɪmə/ Geology and Physical Geography. Now somewhat rare.
1. In any of several theories of the structure of the earth: the lower part of the earth's crust, composed of relatively dense rocks rich in silica and magnesia; spec. (in later use) = oceanic crust n. at oceanic adj. Compounds.Originally, in Eduard Suess's model of the earth, the sima was thought to be completely covered by an outer layer (the sial) of less dense rock. German geophysicist Albert Wegener later identified it as forming a static layer of rock underlying the oceans and continents, positing, in his theory of continental drift, that the continents moved over this. The precise nature of the sima in relation to other parts of the lithosphere was only determined with the advent of the modern theory of plate tectonics, in which it was recognized that the sima (now more usually called the oceanic crust) is split into different sections that, along with sections of the continental crust and rocky mantle, are components of tectonic plates.
ΘΚΠ
the world > the earth > structure of the earth > [noun] > crust > parts of crust
oceanic crust1863
platform1880
sal1909
sima1909
sial1922
ocean crust1927
the world > the earth > structure of the earth > constituent materials > [noun] > material of earth's crust
rock1671
mantle rock1896
sima1909
sial1922
asthenolith1929
pyrolite1962
1909 H. B. C. Sollas & W. J. Sollas tr. E. Suess Face of Earth IV. xv. 544 We assume the existence of three zones..as determining the structure of the earth, namely, the barysphere or the Nife (Ni-Fe), Sima [Ger. Sima] (Si-Mg), and Sal (Si-Al).
1922 Geol. Mag. 59 338 He [sc. Wegener] thinks that the Sal does not cover the globe completely. It now exists in independent patches, which float in the heavier Sima.
1970 Delaware County (Pa.) Daily Times 16 Dec. 42/6 The sial's rocks are granitelike; those in the sima are more like hardened lava.
2002 D. Waugh Geography (ed. 3) i. 14/1 Oceanic crust, or sima, consists of much younger and denser rock of basaltic composition.
2. The rock from which the lower part of the earth's crust is formed, consisting predominantly of relatively dense rock (esp. basalt) rich in silica and magnesia.
ΚΠ
1922 Geogr. Rev. 12 673 The continents being formed of light sial stood higher than the ocean basins, which consisted of sima.
1994 R. Greely Planetary Landscapes (ed. 2) iii. 47/1 Oceanic crust is composed of sima and is relatively thin.
Derivatives
siˈmatic adj. [probably after German simatisch (1915 or earlier)] of, relating to, or constituting the lower layer (the sima) of the earth's crust.
ΘΚΠ
the world > the earth > structure of the earth > [adjective] > crust > parts of
oceanic1863
sial1922
simatic1922
1922 Verhandelingen van het Geologisch-Mijnbouwkundig Genootschap voor Nederland en Koloniën 1920–22 5 117 It is supposed by the greater number of geologists that the plastic simatic magma in its inner regions is not at rest.
1942 R. A. Daly Floor of Ocean ii. 59 The oceanic sectors of the earth are characteristically simatic... Also simatic is any vitreous basalt which may form ‘pockets’ in the crust.
1955 Sci. Amer. Sept. 62/1 Because granite is the chief sialic rock and basalt the chief simatic one, the continents are most commonly described as granitic and the ocean basins as basaltic.
1971 Proc. 2nd Symp. Upper Mantle Project (Council Sci. & Industr. Res., New Delhi) p. xix Resting on the simatic crust, the continental blocks move, as if riding on the conveyor belt.
2012 H. Frankel Continental Drift Controv. I. ii. 56 They formed on the leading edge of drifting continents as they plowed through the simatic ocean floor.
This entry has been updated (OED Third Edition, September 2019; most recently modified version published online March 2022).
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n.1909